Processes and apparatus for continuous solution polymerization

ABSTRACT

The invention relates to processes and plants for continuous solution polymerization. Such plant and processes include a pressure source, a polymerization reactor, downstream of said pressure source, pressure let-down device, downstream of said polymerization reactor, and a separator, downstream of said pressure let-down device, wherein said pressure source is sufficient to provide pressure to said reaction mixture during operation of said process plant to produce a single-phase liquid reaction mixture in said reactor and a two-phase liquid-liquid reaction mixture in said separator in the absence of an additional pressure source between said reactor and said separator.

This application is the National Stage of International Application No.PCT/US01/32299, filed Oct. 17, 2001, which claims the benefit under 35U.S.C. §119(e) of U.S. Provisional Application No. 60/243,192, filedOct. 25, 2000, the entire disclosure of which is incorporated herein byreference.

FIELD OF INVENTION

The invention relates to processes and apparatus for continuous solutionpolymerization. The invention relates especially to such processes andapparatus using single site soluble transition metal catalysts, inparticular those known as metallocene catalysts. The inventionfurthermore relates especially to such processes and apparatus thatprovide for improved control of hydrogen level, and more especially forimproving series reactor operation using single site soluble transitionmetal catalysts.

BACKGROUND OF INVENTION

Continuous solution polymerization processes generally involve theaddition of catalyst to a monomer and solvent mixture. The mixture maybe back-mixed giving a uniform polymer in an environment withsubstantially no concentration gradients. WO 94/00500 (Pannell, et al.)describes a solution polymerization using metallocene in a continuousstirred tank reactor, which may be in a series reactor arrangement tomake a variety of products.

For the purposes of this patent specification the term “metallocene” isherein defined to contain one or more cyclopentadienyl moiety incombination with a transition metal of the Periodic Table of Elements.

The heat of the polymerization reaction can be absorbed by thepolymerization mixture, causing an exotherm. Alternatively, or inaddition, the heat of reaction can be removed by a cooling system, byexternal cooling of the walls of the reactor vessel, or by internallyarranged heat exchange surfaces cooled by a heat exchange fluid.

In the course of the polymerization, typically, a predominant amount(over 50 mol %) of the monomer is consumed and the polymer formed isdissolved in the solvent. The higher the concentration of the polymer,the higher the viscosity of the polymerization reaction mixturecontaining the polymer, solvent, and unreacted components. The mixturepasses from the polymerization reactor to a finishing section in whichpolymer, solvent and unreacted monomer are separated. In the course offinishing, solvent and unreacted monomer are progressively removed fromthe polymerization mixture until the polymer can be formed into a solidpellet or bale. The separated solvent and monomer can be recycled to thepolymerization reactor.

It is well known from extensive literature sources that polymersolutions can undergo phase separation at the lower critical solutiontemperature, with phase separation being encouraged by highertemperatures and/or by lower pressures. Solvents selection alsoinfluences the conditions where phase separation occurs.

The phenomenon of phase separation is firstly a consideration in theselection of the polymerization solvent. Appropriate polymerizationmonomer conversions, especially of the volatile monomers, temperatures,and pressures have to be selected for given polymer/solvent combinationconditions to avoid unwanted phase separation inside the reactor.Solvents such as hexane may require an elevated pressure in excess of 50bar to avoid two-phase conditions for olefin polymerization; solventssuch as octane can maintain homogeneous one-phase conditions at lowerpressures.

The phenomenon of phase separation can secondly be exploited after thereaction step to separate volatile solvent and unreacted monomercomponents on the one hand, and polymer on the other hand. In that case,separation at temperature well above the lower critical solutiontemperature is encouraged to allow the polymer to form a concentratedphase. Some earlier articles explain the general principles of which weare aware are: “A low-energy Solvent Separation Method,” by T. G.Gutowski et al, Polymer Engineering; “Solvents” by C. A. Irani et al. inJournal of Applied Polymer Science Vol 31, 1879-1899 (1986); “SeparatingPolymer Solutions with Supercritical Fluids,” by Mark A. McHugh et al inMacromolecules 1985, 18, 674-680; “Critical dynamics and phaseseparation kinetics etc,” by Hajime Tanaka in Journal of ChemicalPhysics 100 (7) 1 Apr. 1994 p 5323-5337; “Short Chain Branching Effecton the Cloud Point Pressures of Ethylene Copolymers etc.,” by S. J. Hanet al. in Macromolecules 1998, 31, 2533-2538.

U.S. Pat. No. 3,726,843 described a process for making EPDM. Liquidphase separation has also been exploited to remove solvent from thepolymerized mixture exiting from the polymerization reactor in MitsuiEP-552945-A (U.S. Pat. No. 5,599,885), which shows a continuous solutionpolymerization process with a metallocene catalyst. Hydrogen is added inthe examples to avoid higher molecular weights at the low operatingtemperature. The pressure and temperature are raised to permit asubsequent pressure drop, that leads to the formation of separate leanand concentrated phases. Catalyst emerging from the reactor is recycled.

EP-552945-A does not disclose that the polymerization process may beconducted at elevated pressures to provide a wide range of polymers andoutputs in the same plant arrangement. EP-552945-A uses anauto-refrigerated reactor in which the solvent is allowed to boil whichfavors low pressure operation. EP-552945-A does not suggest exploitingthe initial elevated pressure in the finishing section.

While the single site, metallocene catalysts have a high activity; thatactivity is often sustained under conditions in which phase separationwould occur at elevated temperatures. Continued polymerization activityduring phase separation may influence polymer characteristicsundesirably.

The use of single site catalysts is associated with poor solubility inthe aliphatic hydrocarbon, saturated, non-polar solvents used forhomogeneous solution polymerization. As a result, an aromatic catalystsolvent, such as toluene may have to be used. This in turn cancomplicate solvent separation to prevent toluene build up in thereactor, and lead to environmental pollution and added maintenanceexpenditure. EP-552945-A tries to avoid the use of toluene by slurryingthe catalyst, comprising alumoxane as activator, in the polymerizationsolvent.

In some solution processes (see WO 98/02471 Kolthammer) the polymerizedmixture is flashed off in two stages, whereby the solvent and unreactedmonomer are converted to a vapor phase. Efficient extraction of solvent,etc., requires low vapor pressures and vapor phase compression orcondensation followed by pumping for subsequent separation stages.Pumping is used to convey polymer from flash separation stages to afinal devolatilizing extruder

U.S. Pat. No. 3,912,698 uses a heat exchanger for a liquid recyclestream to permit an increase in reactor capacity while reducing foulingin the context of a multiple flash to remove volatiles.

The use of single site catalysts is also associated with the generationof hydrogen through beta-hydride abstraction. Such hydrogen, whenrecycled back to reactor feed, can act as a modifier to reduce themolecular weight of the polymer. The amount of hydrogen established inpolymerization may have to be increased or decreased depending on thetarget molecular weight.

In solution plants, solvent selection, operating temperatures, andpurification systems have to be designed for a particular operatingwindow for the desired polymerization process. Metallocene catalystspermit a wide variety of polymers to be made in terms of comonomercontent, molecular weight, etc. Optimum production performance for agiven type of polymer may be obtained with a particular metallocenewithin a specific operating window. Different types of polymer may thenhave to be produced in different plant lay-outs. There is, therefore, aneed for a plant design that can be used more flexibly for differenttypes of polymers and metallocene catalysts, and which also can beadapted more easily to evolving metallocene catalyst technologies thancurrent designs of solution polymerization plants.

There is also a need for a plant design that permits more extensivemolecular weight control through control of the hydrogen levels. Thereis an special need for such control that is compatible with seriesreactor operation that permits well separated split-operating conditionsbetween the first and second reactor (one which permits feeding very lowlevels of hydrogen to one of the two reactors, while feeding largeamounts of hydrogen to the other reactor).

There remains a need for an improved continuous solution process andplant which provides one or more of the following benefits: producingpolymer economically across a broad range of operating windows includingvarying polymerization temperatures; producing a broad spectrum ofpolymers, particularly polymers of widely varying average molecularweights, molecular weight distributions, and/or comonomer contents;permitting the production of polymers having useful molecular weights athigh temperatures (above 150° C.); accommodating a broad range ofcatalyst performance; reducing energy consumption, especially infinishing, and reducing environmental discharge; and reducing oravoiding fouling in the recycle and purification systems while usinghighly active metallocene type catalysts with unreacted monomer andtemperature during separation processes.

It would be particularly useful to provide a process and plant which canadjust the process window to optimize performance for a given polymertype and catalyst, such that metallocene catalyst can be used to performat a high activity within that window; while at the same time permittinga broad range of optimized performance windows for different polymertypes and catalysts. It would also be beneficial to provide a processand plant which could facilitate operating at such high catalystactivities in the same finishing equipment, which can be used in alargely closed system with substantial recycling of all non-polarsolvent and monomer components; with minimal contamination and minimalneed to eliminate polar impurities contained in such non-polar recycle,however derived (catalyst residue; scavenger, etc), using a simpleremoval technique, and without using a stripping agent such as waterwhich would contaminate the recycle.

For additional background, see also WO 94/00500 and WO92/14766.

SUMMARY OF INVENTION

The numbers shown in brackets refer to the numbering of items shown inthe drawings and intended for illustration and facilitatingunderstanding and are not intended to limit the disclosure to the itemsillustrated.

The invention relates generally to a process for continuous solutionpolymerization of a feed (2, 4, 58) of olefinically unsaturated monomersin a hydrocarbon solvent under pressure, having a continuous stirredtank reactor arrangement (8), to which a single site catalyst issupplied, to form a polymer containing polymerization reaction mixture,and downstream thereof a separating means for continuous separation ofthe solvent (14, 34, 40) and unreacted monomer from the mixture, whichseparating means (14, 34, 40) includes at least an initial liquid phaseseparator to separate the polymerization mixture into a lean phase (20)and a concentrated phase (22). The terms “lean” and “concentrated” or“polymer rich” refers to amount of polymer in the solvent. “Lean”indicates that the solvent contains no polymer or such low amounts ofpolymer so as to not interfere with subsequent recycling.

The catalyst is preferably a bulky ligand transition metal catalyst. Thebulky ligand contains a multiplicity of bonded atoms, preferably carbonatoms, forming a group, which may be cyclic with one or more optionalhetero-atoms. The bulky ligand may be metallocene-type cyclopentadienylderivative, which can be mono- or poly-nuclear. One or more bulkyligands may be bonded to the transition metal atom. The bulky ligand isassumed, according to prevailing scientific theory, to remain inposition in the course of polymerization to provide a homogenouspolymerization effect. Other ligands may be bonded or coordinated to thetransition metal, preferably detachable by a cocatalyst or activator,such as a hydrocarbyl or halogen-leaving group. It is assumed thatdetachment of any such ligand leads to the creation of a coordinationsite at which the olefin monomer can be inserted into the polymer chain.The transition metal atom is a Group IV, V or VI transition metal of thePeriodic Table of Elements. The transition metal atom is preferably aGroup IVB atom.

In a first aspect of the invention a high capacity, low viscosity pump(3) raises the pressure of the feed (2, 4, 58) to at least 75 bar andcauses the mixture to pass from the reactor (8) through a heatingarrangement (12, 16) up to a pressure reducing means (18) upstream ofthe liquid phase separator (14) through the action of the pump (3) andin the absence of further pumping means between the reactor (8) and thepressure reducing means (18). The term “high capacity, low viscositypump” refers generally to a pump with a capacity sufficient topressurize the whole of the feed at a viscosity not affected by thepresence of viscvosity increasing dissolved polymer molecules. Asuitable pump type is a centrifugal pump.

The heating arrangement may comprise a first heating stage (12) and asecond heating stage (16). The first stage (12) is a heat integratingheat exchanger designed to recover heat that would otherwise be lostwhen the lean phase (20) was cooled in a final cooler (24). The secondstage (16) uses any appropriate heat utility of suitable temperature tofinish the heating step.

The reactor arrangement may be single reactor or a plurality,prefereably two, reactors arranged in series, or less preferably inparallel.

In this first aspect, a catalyst killer (10) is added downstream ofreactor arrangement (8) (in the case of series reactors that means thatthe killer is added downstream of the last polymerization reactor) andupstream of the heating arrangement (12, 16) and the liquid phaseseparator to suppress further polymerization of the heatedpolymerization mixture undergoing separation, the lean phase (20) beingpassed through a cooling arrangement, which may comprise the heatintegrating exchanger (12) and a final cooler (24), and optionally adrier (32) back to the inlet side of the pump (3); the concentratedphase (22) being subjected to additional solvent removal downstream toobtain a solid polymer.

In a second aspect the lean phase (20) is passed in liquid form to ameans (26) for removing hydrogen added to or generated duringpolymerization, which means (26) comprises a means for contacting astripping vapor with the lean phase in a countercurrent flow arrangementto concentrate the hydrogen in the vapour phase for removal from thelean phase recycle. This aspect may be practiced in processes and plantsnot employing the features of the first aspect.

DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic lay-out of a plant according to the inventionand a process flow according to the invention.

FIG. 2 shows a phase diagram illustrating the operation of a liquidphase separator used in the plant and process according to theinvention.

FIG. 3 shows the details of the lay-out of a hydrogen strippingarrangement for the plant of FIG. 1 to provide wide ranging molecularweight control.

The numbers in brackets below again refer to the corresponding featuresin the drawings included for illustration and ease of understanding. Theinvention includes other forms of the features indicated by the numbersin brackets in addition to those shown in the drawings as would beapparent to person skilled in the art.

DETAILED DESCRIPTION OF GENERAL AND FIRST ASPECTS

By raising the pressure by the pump (3) to above 75 bar, the formationof two-phase conditions is avoided in the reactor arrangement (8) andheating arrangement (12, 16) under a wide range of temperature andpolymerization conditions. Hence a wide variety of metallocene catalystscan be used in the process. Such a wide range of metallocene catalystscan be used to make high and/or low average molecular weight materialsunder optimized production conditions. Use of a separate pump to boostthe pressure of the viscous polymerization mixture between the reactorand the liquid phase separator can be avoided, [such pumps are much morecostly than the low viscosity feed pump (3)]. The pressure of the pump(3) also cascades through the process and combines with the absence ofvaporization for the initial solvent separating stage to reduce overallpumping needs during finishing. The pressure of the pump (3) advancesthe viscous polymerization mixture to the pressure reducing means (18)upstream of the liquid phase separator (14) without allowing phaseseparation prior to the pressure reducing means (18). In a preferredform of the invention, the pressure of the pump (3) additionallyadvances one or both separated phases to further downstreamfractionating systems or purification devices such as high pressureflash separation devices or low pressure flash separating devices.

The integral killer arrangement permits the temperature to be increasedwithout risking further polymerization so facilitating direct recycle,after removal of any surplus killer, of separated solvent and monomer tothe inlet side of the pump (3). By the term “direct” it is meant thatthe lean phase does not need to be fractionated. The plant can be usedunder a wide variety of conditions to make a wide variety of polymersand is at the same time of simple construction.

Energy consumption per unit polymer produced is low, with simple solventrecovery and energy integration systems [such as heat integratingexchanger (12)], which can be employed to minimize discharges toatmosphere and to recover heat from the effluent on the liquid phaseseparator (14).

Preferably the liquid phase separator (14) is connected to a lowpressure separator (34), arranged downstream, which receives theconcentrated phase from the liquid phase separator (14). Preferably alow-pressure separator (34) operates at a pressure sufficient to allowfeeding of the vapor phase to the fractionating and purification systemwithout requiring a separate compressor, and said pressure is generally2 bar guage or more. In order to accommodate production of polymers witha wide range of molecular weights, this pressure in the low pressureseparator (34) can be raised to a high level, between 3 and 20 bar, toadjust solution viscosity to facilitate feeding of the concentratedpolymer solution to the final devolatizing stage. Thus the volatilephase removed from a concentrated phase is conveyed simply to afractionating tower (36) as a vapor, arranged downstream of the lowpressure separator (34), for purification. In some prior artarrangements where solvents, etc., are drawn off under a low pressure inthe vapor phase, the extracted volatiles must be condensed and passedthrough pumping means for subsequent further separation steps.

Preferably, the process uses a non-polar solvent which does notcoordinate or interfere in a meaningful way so as to inhibit thecatalytic action of the catalyst system. Preferably the process uses alow boiling, alkane based solvent, optionally mixtures of alkanes, whichmay be linear or branched, such as those having from 4 to 10 carbonatoms, preferably in the range of 5-7 carbon atoms, optionally inadmixture with other alkanes of a higher or lower molecular weight. Thepolymer may be derived of monomers predominantly comprising mono-olefinssuch as ethylene or propylene or other higher alpha-olefins having from4 to 10 carbon atoms. This combination provides a mixture which can beeasily separated inside the liquid phase separator.

Considerable energy can be preserved by providing that thepolymerization mixture from the reactor (8) is heated to the temperaturebefore reaching the separator (14) successively by an upstream heatintegration exchanger (12) and a downstream trim heat exchanger (16) andby providing that the lean phase (20) from the separator (14) is used tosupply heat to the upstream one (12) of said heat exchangers.

Working pressures in the process of the invention can be 80 bar or more,90 bar or more; 95 bar or more and especially 120 bar or more, or even140 bar or more. The upper pressure limit is not critically constrainedbut typically can be 200 bar or less, preferably 140 bar or less, or 120bar or less. The pressure should suffice to keep the reactor solution ina single phase up to the point of the pressure reducing means (18), andto provide the necessary working pressure to convey the fluids throughthe plant.

The invention in another aspect also relates to a plant adapted toperform the process described above which is suited to operate withinthe performance envelopes indicated below and with the SSC indicatedbelow. More aspects will be apparent from the claims.

The feed temperature may vary depending on the available exotherm andextent of monomer conversion desired to reach the polymerizationtemperature. Advantageously the temperature is at least minus 40° C.,suitably, at least −20° C., 0° C., 20° C. or 40° C. in certaincircumstances. The polymerization temperature is constrained by themolecular weight desired, allowing for the influence of any hydrogenadded. In a series reactor process the temperature in the successivereactors can be raised progressively in increments depending on thenature of the polymerization taking place in such reactors.Advantageously, the polymerization temperature for polymers comprisingpredominantly ethylene derived units is at least 100° C., preferably atleast 150° C. or even (for lower molecular weight materials) 200° C. ormore. The temperature should not exceed the polymerization decompositiontemperature or the temperature at which the catalyst can sustain thepolymerization reaction.

Overall the exotherm may lead to a temperature differential between theinlet temp of the polymerization reactor and the outlet of from 50 to220 or up to 250° C. By feeding at minus 40° C. and allowing theexotherm to raise the temperature to 210° C., a highly efficient processmay result for producing lower molecular weight polymers. For highermolecular weight polymers, the temperature rise may need to beconstrained via warmer feed and/or lower reactor temperatures to avoidexcessive viscosity in the reactor solution that would degrade reactormixing performance, thereby leading to non-uniform polymers.

Monomer concentration depends on the target polymer type and molecularweight, the associated conversions of monomer to polymer and operatingtemperature. Advantageously, the monomer partial pressure should be 30%or more of the total partial pressure of volatile components in thepolymerization reactors; especially 40% or more, and should preferablynot exceed 80%, 70% or especially 60%. The total partial pressure of allcomponents should be less than 100% of the reactor pressure to avoidformation of vapor bubbles. In general, higher monomer partial pressuresare preferred to improve the liquid phase separation in the liquid phaseseparator (14).

In its broadest form, the invention can be performed with any SSC(single sited catalyst). These generally contain a transition metal ofGroups 3 to 10 of the Periodic Table; and at least one ancillary ligandthat remains bonded to the transition metal during polymerization.Preferably the transition metal is used in a cationic state andstabilized by a cocatalyst or activator. Especially preferred aremetallocenes of Group 4 of the Periodic table such as titanium, hafniumor zirconium which are used in polymerization in the d⁰ mono-valentcationic state and have one or two ancillary ligands as described inmore detail hereafter. The important features of such catalysts forcoordination polymerization are the ligand capable of abstraction andthat ligand into which the ethylene (olefinic) group can be inserted.

The metallocene can be used with a cocatalyst which may be alumoxanepreferably methylalumoxane having an average degree of oligomerizationof from 4 to 30 as determined by vapor pressure osmometry. Alumoxane maybe modified to provide solubility in linear alkanes or be used in aslurry but is generally used from a toluene solution. Such solutions mayinclude unreacted trialkyl aluminum and the alumoxane concentration isgenerally indicated as mol Al per liter, which figure includes anytrialkyl aluminum which has not reacted to form an oligomer. Thealumoxane, when used as cocatalyst, is generally used in molar excess,at a mol ratio of 50 or more, preferably 100 or more, and preferably1000 or less, preferably 500 or less, relative to the transition metal.

The SSC should preferably be selected from among a broad range, ofavailable SSC's, to suit the type of polymer being made and the processwindow associated therewith in such a way that the polymer is producedunder the process conditions at an activity of at least 40,000 g polymerper gram SSC (such as a metallocene), preferably at least 60,000 or evenin excess of 100,000 g polymer per g SSC. This specification andexamples exemplify some of the options. By enabling the differentpolymers to be produced in different operating windows with an optimizedcatalyst selection, the SSC and any ancillary catalyst components can beused in small quantities, with optionally also using small amounts ofscavengers. The killer can be used in equally small amounts and thevarious cost-effective methods can then be introduced to allow thenon-polar solvent to be recycled and subjected to treatment to removepolar contaminants before re-use in the polymerization reactor(s).

The metallocene may be also be used with a cocatalyst which is a non- orweakly coordinated anion (the term non-coordinating anion as used hereinincludes weakly coordinated anions. The coordination should besufficiently weak in any event, as evidenced by the progress ofpolymerization, to permit the insertion of the unsaturated monomercomponent.) The non-coordinating anion may be supplied and reacted withthe metallocene in any of the manners described in the art.

The precursor for the non-coordinating anion may be used with ametallocene supplied in a reduced valency state. The precursor mayundergo a redox reaction. The precursor may be an ion pair of which theprecursor cation is neutralized and/or eliminated in some manner. Theprecursor cation may be an ammonium salt as in EP-277003 and EP-277004.The precursor cation may be a triphenylcarbonium derivative.

The non-coordinating anion can be a halogenated, tetra-aryl-substitutedGroup 10-14 non-carbon element-based anion, especially those that arehave fluorine groups substituted for hydrogen atoms on the aryl groups,or on alkyl substituents on those aryl groups.

The effective Group 10-14 element cocatalyst complexes of the inventionare, in a preferable embodiment, derived from an ionic salt, comprisinga 4-coordinate Group 10-14 element anionic complex, where A⁻ can berepresented as:

 [(M)Q₁Q₂ . . . Q_(i)]⁻,

where M is one or more Group 10-14 metalloid or metal, preferably boronor aluminum, and each Q is a ligand effective for providing electronicor steric effects rendering [(M′)Q₁Q₂ . . . Q_(n)]⁻ suitable as anon-coordinating anion as that is understood in the art, or a sufficientnumber of Q are such that [(M′)Q₁Q₂ . . . Q_(n)]⁻ as a whole is aneffective non-coordinating or weakly coordinating anion. Exemplary Qsubstituents specifically include fluorinated aryl groups, preferablyperfluorinated aryl groups, and include substituted Q groups havingsubstituents additional to the fluorine substitution, such asfluorinated hydrocarbyl groups. Preferred fluorinated aryl groupsinclude phenyl, biphenyl, naphthyl and derivatives thereof.

The non-coordinating anion may be used in approximately equimolaramounts relative to the transition metal component, such as at least0.25, preferably 0.5, and especially 0.8 and such as no more than 4,preferably 2 and especially 1.5.

Representative metallocene compounds can have the formula:L^(A)L^(B)L^(C) _(i) MDEwhere, L^(A) is a substituted cyclopentadienyl orhetero-cyclopentadienyl ancillary ligand π-bonded to M; L^(B) is amember of the class of ancillary ligands defined for L^(A), or is J, ahetero-atom ancillary ligand σ-bonded to M; the L^(A) and L^(B) ligandsmay be covalently bridged together through a Group 14 element linkinggroup; L^(C) _(i) is an optional neutral, non-oxidizing ligand having adative bond to M (i equals 0 to 3); M is a Group 4 or 5 transitionmetal; and, D and E are independently mono-anionic labile ligands, eachhaving a σ-bond to M, optionally bridged to each other or L^(A) orL^(B.) The mono-anionic ligands are displaceable by a suitable activatorto permit insertion of a polymerizable monomer or macro-monomer caninsert for coordination polymerization on the vacant coordination siteof the transition metal component.

Representative non-metallocene transition metal compounds usable asSSC's also include tetrabenzyl zirconium, tetra bis(trimethylsiylmethyl)zirconium, oxotris(trimethlsilylmethyl) vanadium, tetrabenzyl hafnium,tetrabenzyl titanium, bis(hexamethyl disilazido)dimethyl titanium,tris(trimethyl silyl methyl) niobium dichloride, andtris(trimethylsilylmethyl) tantalum dichloride.

Additional organometallic transition metal compounds suitable as olefinpolymerization catalysts in accordance with the invention will be any ofthose Group 3-10 that can be converted by ligand abstraction into acatalytically active cation and stabilized in that active electronicstate by a non-coordinating or weakly coordinating anion sufficientlylabile to be displaced by an olefinically unsaturated monomer such asethylene.

More preferred are metallocenes which are biscyclopentadienylderivatives of a Group IV transition metal, preferably zirconium orhafnium. See ExxonMobil WO9941294. These may advantageously bederivatives containing a fluorenyl ligand and a cyclopentadienyl ligandconnected by a single carbon and silicon atom. See ExxonMobil WO9945040;and WO9945041 and. Most preferably the Cp ring is unsubstituted and/orthe bridge contains alkyl substituents, suitably alkylsilyl substituentsto assist in the alkane solubility of the metallocene. See WO0024792 andWO0024793. Other possible metallocenes include those in WO01/58912

Dow EP418044 uses a monocyclopentadienyl compound similar that thatEP416815. Similar compounds are described in ExxonMobil EP-420436.Sumitomo WO9703992 shows a catalyst in which a single Cp species and aphenol are linked by a C or Si linkage, such asMe2C(Cp)(3-tBu-5-Me-2-phenoxy)TiCl2. Nova WO200105849 disclosesCp-phosphinimine catalysts, such as (Cp)((tBu)3P═N—)TiCl2.

Other suitable metallocenes may be bisfluorenyl derivatives or unbridgedindenyl derivatives which may be substituted at on eor more positions onthe fused ruing with moieties which have the effect of increasing themolecular weight and so indirectly permit polymerization at highertemperatures such as described in EP693506 and EP780395.

When using the catalysts of the invention, the total catalyst systemwill generally additionally comprise one or more organometalliccompounds as scavenger. Such compounds as used in this application ismeant to include those compounds effective for removing polar impuritiesfrom the reaction environment and for increasing catalyst activity.Impurities can be inadvertently introduced with any of thepolymerization reaction components, particularly with solvent, monomerand catalyst feed, and adversely affect catalyst activity and stability.It can result in decreasing or even elimination of catalytic activity,particularly when ionizing anion pre-cursors activate the catalystsystem. The impurities, or catalyst poisons include water, oxygen, polarorganic compounds, metal impurities, etc. Preferably steps are taken toremove these poisons before introduction of such into the reactionvessel, for example by chemical treatment or careful separationtechniques after or during the synthesis or preparation of the variouscomponents, but some minor amounts of organometallic compound will stillnormally be used in the polymerization process itself.

Typically these compounds will be organometallic compounds such as theGroup-13 organometallic compounds of U.S. Pat. Nos. 5,153,157, 5,241,025and WO-A-91/09882, WO-A-94/03506, WO-A-93/14132, and that of WO95/07941. Exemplary compounds include triethyl aluminum, triethylborane, tri-isobutyl aluminum, tri-n-octyl aluminum, methylalumoxane,and isobutyl alumoxane. Alumoxane also may be used in scavenging amountswith other means of activation, e.g., methylalumoxane andtri-isobutyl-aluminoxane with boron-based activators. The amount of suchcompounds to be used with catalyst compounds of the inventions isminimized during polymerization reactions to that amount effective toenhance activity (and with that amount necessary for activation of thecatalyst compounds if used in a dual role) since excess amounts may actas catalyst poisons.

The process and the plant used in the process are designed as explainedabove to permit polymerization of a wide variety of polymer types andmolecular weights. Generally speaking the polymers are derived fromeither ethylene or propylene as the dominant (more than 50 mol %)component. Polymers may preferably contain from 5 to 40 mol % ofcomonomer to vary crystallinity and flexibility. The comonomers may bealpha-olefins (under which term cyclic olefins such as styrene areincluded) having from 2 to 20 carbon atoms, such as ethylene (in thecase of the polymer consisting predominantly of propylene derived units)butene-1, hexene-1, octene-1. Amounts of dienes such as hexadiene, vinylnorbornene, ethylidene norbornene (ENB), norbornadiene etc may beincluded to promote unsaturation and/or the formation of longer branchesthemselves made from polymerized monomer derived units.

In the case of plastomer, the polymer which may be produced include thefollowing aspects: Preferably the comonomer is an alpha-olefin havingfrom 3 to 15 carbon atoms, more preferably 4 to 12 carbon atoms and mostpreferably 4 to 10 carbon atoms. Ethylene can be polymerized with atleast two comonomers to form a terpolymer. Monomer is generallypolymerized in a proportion of 70.0-99.99, preferably 70-90 and morepreferably 80-95 or 90-95 mole % of ethylene with 0.01-30, preferably3-30 and most preferably 5-20 mole % comonomer. For the purposes of thispatent specification the molecular weight distribution of a polymer canbe determined with a Waters Gel Permeation Chromatograph equipped withUltra-styrogel 5 columns and a refractive index detector. The operatingtemperature of the instrument was set at 145° C., the eluting solventwas trichlorobenzene, and the calibration standards included sixteenpolystyrenes of precisely known molecular weight, ranging from amolecular weight of 500 to a molecular weight of 5.2 million, and apolyethylene standard, NBS 1475. 10. The molecular weight distributionof the plastomers produced in this invention are termed “narrow” that isto say an M_(w)/M_(n) less than 3, preferably less than or equal to 2.5.The MI of the polymers of the invention are generally in the range of0.01 dg/min to 200 dg/min, preferably 0.1 dg/min to 100 dg/min, morepreferably 0.2 to 50 dg/min and most preferably less than 10 dg/min.Contemplated densities of component A of the invention are in the rangeof 0.85 to 0.93 g/cm³, preferably 0.87 to 0.92 g/cm³, more preferably0.88 to 0.91 g/cm³.

The invention can be especially concerned with copolymerizationreactions involving the polymerization of one or more of the monomers,for example alpha-olefin monomers of ethylene, propylene, butene-1,pentene-1 1,4-methylpentene-1, hexene-1, octene-1, decene-1 and cyclicolefins such as styrene. Other monomers can include polar vinyl, dienes,norbornene, acetylene and aldehyde monomers.

In the case of elastomers, the polymer which may be produced includeterpolymers of an ethylene-a-olefin-EODE (Ethylene-alpha-Olefin-DieneElastomer) of high M_(w) and greater than 0.3 weight % diene content,preferably greater than 2.0 weight % diene content. These polymers maybe largely amorphous and have a low or zero heat of fusion. As usedherein the term “EODE” encompasses elastomeric polymers comprised ofethylene, an a-olefin, and one or more non-conjugated diene monomers.The non-conjugated diene monomer can be a straight chain, branched chainor cyclic hydrocarbon diene having from 6 to 15 carbon atoms. Examplesof suitable non-conjugated dienes are straight chain acyclic dienes suchas 1,4-hexadiene and 1,6-octadiene; branched chain acyclic dienes suchas 5-methyl-1,4-hexadiene; 3,7-dimethyl-1,6-octadiene;3,7-dimethyl-1,7-octadiene and mixed isomers of dihydromyricene anddihydroocinene; single ring alicyclic dienes such as 1,4-cyclohexadiene;and 1,5-cyclododecadiene; and multi-ring alicyclic fused and bridgedring dienes such as tetrahydroindene, methyl tetrahydroindene,dicyclopentadiene; bicyclo-1 5 (2,2,1)-hepta-2,5-diene; alkenyl,alkylidene, cycloalkylidene norbornenes such as 5-methylene-2-norbornene(MNB); 5-propenyl-2-norbornene, 5-isopropylidene-2-norbornene,5-(4-cyclopentenyl)-2-norbornene, 5-cyclohexylidene-2-norbornene,5-vinyl-2-norbornene and norbornadiene.

Of the dienes typically used to prepare EPDMs, the particularlypreferred dienes are, 1,4-hexadiene (HD), 5-ethylidene-2-norbornene(ENB), 5-vinylidene-2-norbornene (VNB), 5-methylene-2-norbornene (MNB),and dicyclopentadiene (DCPD). The especially preferred dienes are5-ethylidene-2-norbornene (ENB) and 1,4-hexadiene (HD). The preferredEOD elastomers may contain 20 up to 90 weight % ethylene, morepreferably 30 to 85 weight % ethylene, most preferably 35 to 80 weight %ethylene. The alpha-olefin suitable for use in the preparation ofelastomers with ethylene and dienes are preferably propylene, 1-butene,1-pentene, 1-hexene, 1-octene and 1-dodecene. The alpha-olefin isgenerally incorporated into the EODE polymer at 10 to 80 weight %, morepreferably at 20 to 65 weight %. The non-conjugated dienes are generallyincorporated into the EODE at 0.5 to 20 to 35 weight %; more preferablyat 1 to 15 weight %, and most preferably at 2 to 12 weight %. Ifdesired, more than one diene may be incorporated simultaneously, forexample HD and ENB, with total diene incorporation within the limitsspecified above.

The elastomers may also be devoid of a diene and be a copolymer of twomonomer types. Such copolymers may be elastomers of high M_(w), lowcrystallinity, and low ash. The copolymers may be ethylene-alpha-olefincopolymers (EPC) of high M_(w). As used herein the term “EPC” means acopolymer of ethylene and an alpha-olefin, not necessarily propylene,which exhibits the properties of an elastomer. The alpha-olefinssuitable for use in the preparation of elastomers with ethylene arepreferably C₃-C₁₀ alpha-olefins. Illustrative non-limiting examples ofsuch a-olefins are propylene, 1-butene, 1-pentene, 1-hexene, 1-octeneand 1-dodecene. If desired, more than one alpha-olefin may beincorporated. The EPC elastomers may contain 20 up to 90 weight %ethylene, more preferably 30 to 85 weight % ethylene, and mostpreferably 35 to 80 weight % ethylene.

In the case of polymers derived predominantly from propylene derivedunits, the polymers have the following features as a result of thepresence of isotactic polypropylene sequences in the chain:

In one embodiment, a copolymer of propylene and at least one comonomer,the comonomer being ethylene or an alpha-olefin. Comonomers includeethylene and linear or branched C₄ to C₃₀ alpha-olefins, or combinationsthereof. Preferred linear alpha-olefins include ethylene and C₄ to C₈alpha-olefins, more preferably ethylene, 1-butene, 1-hexene, and1-octene, even more preferably ethylene or 1-butene. Preferred branchedalpha-olefins include 4-methyl-1-pentene, 3-methyl-1-pentene, and3,5,5-trimethyl-1-hexene. The propylene copolymer of the SPC ispreferably a random copolymer, as the term is defined herein below.

The polypropylene copolymer has a crystallinity of from 2% to 65%.Within this range of crystallinity, alternative lower limits ofcrystallinity can be 5% or 10%, and alternative upper limits ofcrystallinity can be 50%, 45% or 40%.

The crystallinity of the polypropylene copolymer of the SPC is derivedfrom isotactic (or alternatively syndiotactic) polypropylene sequencesin the copolymer. The amount of propylene in the SPC can be from 65% to95% by weight. Within this range, alternative lower limits of propylenecontent in the SPC can be 70% or 80% by weight, and alternative upperlimits of propylene content can be 92.5%, 90%, or 89% by weight.

The semi-crystalline polypropylene copolymer necessarily has a non-zeroheat of fusion, due to the measurable crystallinity. The crystallinitycan be calculated from the heat of fusion, using a preferred value of189 J/g for 100% crystallinity and a linear relationship between heat offusion and crystallinity; see, B. Wunderlich, “Macromolecular Physics,”vol. 3, Academic Press (1980), esp. Chapter 8.4.2.

The polypropylene copolymer of the SPC preferably has a single broadmelting transition. Typically, a sample of the polypropylene copolymerwill show secondary melting peaks or shoulders adjacent to the principalpeak, and this combination is considered together as single meltingpoint, i.e., a single broad melting transition. The highest of thesepeaks is considered the melting point. The polypropylene copolymerpreferably has a melting point of from 25° C. to 110° C. Within thisrange, alternative lower limits of the melting point can be 30° C. or35° C., and alternative upper limits of the melting point can be 105° C.or 90° C.

The weight average molecular weight of the polypropylene copolymer canbe from 10,000 to 5,000,000 g/mol, preferably 80,000 to 500,000. The MWD(M_(w)/M_(n)) is preferably above 2. The MWD (M_(w)/M_(n)) may be lessthan 40, more preferably less than 5 and most preferably less than 3. Inanother embodiment, it is preferred that the polypropylene copolymer hasa ML (1+4)@125° C. less than 100, more preferably less than 75, evenmore preferably less than 60, most preferably less than 30.

The polypropylene copolymer of the present invention preferably is arandom, crystallizable copolymer having a narrow compositionaldistribution. The intermolecular composition distribution of the polymeris determined by thermal fractionation in a solvent. A typical solventis a saturated hydrocarbon such as hexane or heptane. The thermalfractionation procedure is described below. Typically, approximately 75%by weight and more preferably 85% by weight of the polymer is isolatedas one or two adjacent, soluble fractions, with the balance of thepolymer in immediately preceding or succeeding fractions. Each of thesefractions has a composition (wt. % ethylene content) with a differenceof no greater than 20% (relative) and more preferably no greater than10% (relative) from the average weight % ethylene content of thepolypropylene copolymer. For purposes of the present disclosure, thepolypropylene copolymer is considered to have a “narrow” compositionaldistribution if it meets the fractionation test outlined above.

The length and distribution of stereoregular propylene sequences inpreferred polypropylene copolymers is consistent with substantiallyrandom statistical copolymerization. It is well known that sequencelength and distribution are related to the copolymerization reactivityratios. As used herein, the term “substantially random” means acopolymer for which the product of the reactivity ratios is generally 2or less. In contrast, in stereoblock structures, the average length ofPP sequences is greater than that of substantially random copolymerswith a similar composition. Prior art polymers with stereoblockstructure have a distribution of PP sequences consistent with these“blocky” structures rather than a random, substantially statisticaldistribution.

The reactivity ratios and sequence distribution of the polymer may bedetermined by C-13 NMR, which locates the ethylene residues in relationto the neighboring propylene residues. To produce a crystallizablecopolymer with the required randomness and narrow compositiondistribution, it is desirable to use: (1) a single-sited catalyst; and(2) a well-mixed, continuous flow, stirred tank polymerization reactorwhich allows only a single polymerization environment for substantiallyall of the polymer chains of preferred polypropylene copolymers.

As general guidance when the molecular weight of the polymers is toolow, liquid phase separation in the manner described herein may behindered or made inefficient as an excessive amount of polymer mightthen be carried over in the lean phase. The precise boundary depends onsolvent composition and polymer composition as well as molecular weight.A rapid pressure let-down, generally greater than 20 bar/second,preferably 30 bar/second or more, more preferably 40 bar/second or more,even more preferably 50 bar/second or more, assists in inducingdisengagement of the two phases. This rapid pressure decrease preferablystarts from a pressure above the binodal boundary or LSCT and stops at apressure below the spinodal boundary. The preferred phase separation isby spinodal decomposition and is called pressure induced phaseseparation (PIPS). Also the liquid phase separator should provide asufficient residence time to permit the settlement of the lean andconcentrated phase at the lower end of the separator.

In the second aspect of the invention, molecular weight control isexercised through control of hydrogen levels, which may be supplementaryto control of molecular weight by control of the polymerizationtemperature. In the second aspect the lean phase is passed in liquidform to a means for removing hydrogen added to or generated duringpolymerization, which means comprises a means for contacting a strippingvapor with the lean phase in a countercurrent flow arrangement toconcentrate the hydrogen in the vapour phase for removal from the leanphase recycle.

The stripping vapor preferably consists of a volatile monomer such asethylene (25). The means may include a stripping vessel (26) to removehydrogen from the recovered solvent stream for use as the polymerizationfeed (2). The stripping vapor advantageously has a low hydrogen content,preferably below 5 mppm. The stripping vapor may be selected to be morevolatile than other monomer or solvent components, be substantiallydevoid of contaminants that are deleterious to the polymerizationcatalysts, be recoverable in the plant recovery system, and preferablybe available at high enough supply pressure for introduction into thestripping vessel (26) without the aid of separate additionalcompression.

This aspect of the invention is especially applicable to plant lay-outswhere reactors are arranged to operate in series and where the upstreamreactor is operated under no or low hydrogen conditions to provide ahigher molecular weight fraction and where hydrogen is added to adownstream reactor to provide a lower molecular weight fraction.

EXAMPLE

With reference to FIG. 1 the plant is arranged as follows:

Polymerization and Initial Separation of Polymer and Solvent

A feed for polymerization is passed through conduit (2) by a centrifugalpump (3). The feed contains A) hexane as solvent, B) monomer, generallythe predominant monomer is ethylene or propylene, and C) comonomer whichmay be any copolymerizable alpha-olefin, and D) a diene or other polyeneor cyclic copolymerizable material. The feed is passed through a chilleror cooler (6) in which the feed is optionally chilled to a lowtemperature for subsequent adiabatic polymerization in the twocontinuous stirred tank reactors (8) which are operated in series (forsimplicity, only one reactor is depicted in FIG. 1). Activator andmetallocene catalyst may be premixed and added at (5) and/or (7) to oneor both reactors (8). A scavenger, generally in the form of an alkylaluminum such as tri-isobutyl aluminum or tri-n-octyl aluminum is nextadded at (4) to minimize the impact of poisons in the feed and in thereactor on the catalyst activity.

To complement the molecular weight control provided by controlling thepolymerization temperature, hydrogen may be added to one or bothreactors through conduits (not shown).

The solution, containing polymer, which emerges from the reactors (8)through a conduit (11), is first treated with a catalyst killer,preferably water, added at (10) in a molecular solution in hexanesolvent to terminate the polymerization reaction. A heat exchanger (12)is arranged as part of a heat integrating arrangement and heated by alean phase emerging from an upper layer (20) in a liquid phase separator(14), and provides an initial increase in the temperature of the polymersolution in the conduit (11). A trim heat exchanger (16), operating byusing steam, hot oil or other high temperature fluid, further increasesthe temperature to a level suitable for liquid phase separation. Thesolution then passes through a let down valve (18) where a pressure dropis created which causes the separation of the polymer solution andsettlement into the lean phase (20) and a polymer rich phase (22) belowit.

It is important to note that no energy consuming pump is required toprovide a pressure increase in the conduit (11) between the reactors (8)and the separator (14) as the polymer containing solution is propelledby the pressure from the pump (3).

Treatment of Lean Phase

The lean phase (20), after being cooled by the heat exchanger (12),aforementioned, is cooled further by a cooling device (24), passedthrough a surge tank (26) adapted for stripping out the hydrogen andthen submitted to in-line chemical analysis at (41) to determine theconcentration of monomer and comonomer in the solvent. This cooled leanphase is combined with fresh feed of solvent and monomer (30) to providethe desired concentrations and then passed through a drier (32) whichserves to remove any unreacted water used as the catalyst killer orpresent in the fresh feed supplied or any impurity in the recycledsolvent and monomer as will be explained.

The surge tank (26) is arranged in the form a vessel (26) suitable forstripping out hydrogen by means of ethylene as a stripping vapor as isshown in FIG. 3. The lean phase issuing from the cooler (24) is passedthrough a conduit (27) to a liquid distributor arrangement (100) locatedinside the vessel (26) in an overhead space in an upper part thereof.The liquid distributor consists of a performated pipe distributor withholes (102) on the bottom. The distributor sprays the lean phasedownward inside the vessel (26). Lean phase collects in the lower partof the vessel (26). Part of the ethylene to be added to the feed conduit(2) is supplied as stripping vapor through line (25). The strippingvapor is supplied to a vapor sparger arrangement (104) located insidethe vessel (26) submerged in the lean phase collected in the lower partof the vessel. The vapor sparger consists of multiple disks ofmicroporous media (103) arranged on a plurality of rings, arrangedconcentrically. Vapor bubbles rise from the vapor sparger arrangement(104) through the liquid to the surface into the overhead space. Thevapor in the overhead space is passed through conduit (108) for furthertreatment as described below. The liquid in the lower part is passedthrough conduit (110) for treatment as will be described below.

In the vessel (26) a countercurrent flow of the liquid feed (27) and thestripping vapor (25) occurs. At the stage where the bubbles of strippingvapor rise through the liquid, the ethylene in the vapor is dissolved inthe liquid and hydrogen in the liquid is taken up by the bubbles. Hencethe liquid issuing through conduit (110) is enriched by ethylene whichcan be subjected to polymerization when recycled. A first equilibriumstage can so be approximated. In the vessel (26) vapor space, the risingvapor extracts more hydrogen from the atomized droplets issuing from thenozzles (102) so that a second equilibrium stage can be approximated.The vapor issuing through conduit 108 thus contains a large proportionof the hydrogen contained in the liquid introduced though nozzles 102.Substantially 2 equilibrium stages of separation can be achieved in asingle flash vessel. Over 90%, sometimes over 97%, of the hydrogenpresent in the lean phase can be removed in this way.

The stripping vapor supplied is ethylene, which is a volatile monomerindigenous to the process. Its use minimizes additional operating costsand raw material consumption.

The vapor from conduit (108) is routed to the reflux drum (39) of tower(36). Partly it is processed to recover valuable components, principallyvolatile monomers such as ethylene and propylene, by fractionating tower(36) and its overhead vapor compression/condensation system (37) forrecycling through conduit (43) to the inlet side of the drier (32). Thepart mainly comprising hydrogen and any other non-condensables may beflared at (112).

A less preferred alternative is for part of the lean phase recycle to beflashed in a single stage flash vessel without the addition of strippingvapor. This, however, only permits limited hydrogen removal and detractsfrom the benefit of recycling the lean phase in its liquid state withoutenergy intensive evaporation processes.

In single reactor and in series reactor arrangements using metallocenecatalysts systems varying amounts of hydrogen may be produced bybeta-hydride abstraction, even when no hydrogen is injected into thereactor. The amount may vary with metallocene selected. Its molecularweight reducing effect may be accommodated by appropriate selection ofthe reactor operating temperature. A substantial amount of this hydrogenmay remain unreacted in the reactor effluent stream (11). Reducing theamount of hydrogen recycled in this stream in the manner described abovemay be is advantageous to permit adjustment of the molecular weightindependent of the polymerization operating temperature by removal ofthe generated hydrogen or by addition of hydrogen from an externalsource, generally in the feed conduit (2).

In series reactor operation as described herein, the ability to removehydrogen can be exploited advantageously to widen the molecular weightsplit between the reactors and to broaden the molecular weightdistribution beyond what would otherwise be possible. The feed suppliedto the upstream reactor can have a hydrogen content below that whichwould prevail if hydrogen generated by beta hydride elimination remainedin the recycle. Additional extraneous hydrogen can be added to thedownstream reactor to provide a hydrogen content above that which wouldremain if hydrogen from beta hydride elimination were to remain in therecycle.

Effective removal of the hydrogen thus provides a facility which enablesthe range of bimodal compositions produced in series reactor layouts tobe increased. It also permits the selection of a broader range ofmetallocene catalyst systems regardless of their tendency to generatehydrogen through beta hydride elimination or their sensitivity to thepresence of hydrogen in the polymerization mixture.

Treatment of Polymer Rich Phase

The concentrated polymer rich phase is passed to a low-pressureseparator (34) where evaporated solvent and monomer are separated fromthe more concentrated polymer solution emerging from the liquid phaseseparator (14).

The evaporated solvent and monomer phase is passed through conduit (35)in a vapor phase to the purification tower (36) operating bydistillation to separate a light fraction of the highly volatile solventand unreacted ethylene and propylene on the one hand and heavier lessvolatile components such as hexane and any toluene used to dissolvecatalyst or activator and unreacted diene type comonomers on the otherhand. Use of toluene can be reduced under appropriate circumstances by asuitable selection of catalyst components and catalyst preparationconditions such as increases in catalyst solution temperature toincrease the solubility of the catalyst components to reach a pointwhere so little toluene is present that no separate process for theremoval of the toluene are required.

A gear pump (38) conveys the by now even more concentrated polymer to avacuum devolatilizing extruder or mixer (40), where again a vapor phaseis drawn off for purification, condensed and then pumped to apurification tower (50). A heavy fraction of toluene (52) used ascatalyst solvent and diene such as ethylene norbornadiene (ENB)comonomer or octene-1 comonomer are recovered by this purification tower(50). The ENB or octene can be recycled through outlet (54). Alternativeheavy comonomers, such as ENB and octene, may thereby be stored inseparate storage vessels (55, 56), which facilitates rapid producttransitions between different product families (e.g. EP(D)M and EOplastomers, while still enabling eventual recovery of the valuableunreacted comonomers. This capability further enhances the flexibilityof this process to produce a wide variety of dissimilar products.

The polymer melt emerging from (40) can then be pelletized in anunderwater pelletizer, fed with water chilled at (42), washed and spundried at (44) to form pellets suitable for bagging or baling at (46).

Polymerization of Differing Polymers

The operation of the plant can be best described with reference to theTable 1 on the following page. This takes as examples polymerizationprocesses to make a low molecular weight plastomer (as describedgenerally above); a higher molecular weight elastomer (as describedabove) and a high propylene content ethylene copolymer polymerized asdescribed above.

TABLE 1 Process Conditions of the Plant/Process of the Invention inVarying Operating Modes Polymer Polymer Amount of Solution SolutionPolymer Devolatilized Polymerization Upstream Let- Downstream LeanPolymer Rich Polymer from Feed Into Reactor Inside Reactor Down ValveLet-Down Valve Phase Phase Extruder Plastomer 0 or down to - 150-200°C.; 220° C.; 40 or 220° C; 40 bar; 220° C.; 40 220° C.; 40 bar; High 15°C.; 120 bar 100 or 120 bar; 100 bar; 15-22 15-22 wt % bar; <0.1 wt 30-40wt % total; 50 bar 15-22 wt % wt % polymer polymer % polymer polymermonomer partial polymer pressure. Elastomer 0 or down to - 100° C.; 100or 220° C.; 100 bar; 220° C.; 40 bar; 220° C.; 40 220° C.; 40 bar;Medium 15° C.; 120 bar 120 bar; 8-12 8-12 wt % 8-12 wt % bar; <0.1 wt 30wt % total; 50 bar wt % polymer polymer polymer % polymer polymermonomer partial pressure. Predominant 0 or down to - 50 or 60° C.; 200°C.; 100 bar; 200° C.; 40 bar; 200° C.; 40 220° C.; 40 bar; Low Propylene15° C.; 120 bar 120 bar; 7-8 7-8 wt % 7-8 wt % bar; <0.1 wt 30-35 wt %Content total; 50 bar wt % polymer polymer polymer % polymer polymerCopolymer monomer partial pressure.

To make plastomer in FIG. 1, the feed temperature is reduced by thechiller (6) to 0° C. Aluminum alkyl is added as scavenger in amountsappropriate to the poison content of the feed. Alternatively the processof WO9722635 (Turner et al.) incorporated herein for US purposes. Thepressure is raised by the centrifugal pump to 120 bar. The feedcomprising largely solvent and up to 50 bar partial pressure of ethyleneand butene or hexene or octene comonomer then enters the first of thetwo series reactors (8). Catalyst and activator is added to the reactors8 in amounts to create the desired polymerization temperature which inturn is related to the desired molecular weight. The heat ofpolymerization increases the temperature to 150 to 200° C. to form aplastomer without the use of hydrogen (although H₂ may be used). At theoutlet of the second series reactor, the polymer concentration is in therange of from 15-22 wt %. The general conditions may be as described inWO 99/45041 incorporated herein for US purposes.

Water is then supplied at (10) to kill the polymerization reaction whichmight otherwise continue in the presence of surviving catalyst,unreacted monomer, and elevated temperature.

The heat exchanger (12) raises the temperature initially and then thefurther heat exchanger (16) causes a further temperature rise to 220° C.A rapid pressure drop results as the polymerization mixture passesthrough the let-down valve (18) into the liquid phase separator, withthe pressure dropping quickly from 100 Bar to 40 bar. The pressuredifferential between that at the outlet of the pump (3) and the outletof the let down valve 18 is solely responsible for causing the feed andthe polymerization mixture to flow through the reactor (8) and theconduit (11) including the heat exchangers (12) and (16).

The details of liquid phase separation by passing through a lowercritical solution temperature (LCST) boundary is explained withreference to FIG. 2. Polymerization takes place at 100 or 120 bar in thepolymerization reactor(s) at the pressure also prevailing upstream ofthe pressure letdown device at a level as shown by line A. Thetemperature is maintained and/or raised to a range marked by the bracketshown at B to between 150 and 200 or 220° C. At the prevailingtemperature, the pressure is dropped along the arrow to a level markedX. As the temperature is dropped across the letdown valve from 100 barto 40 bar, the polymerization mixture passes from a homogeneous singlephase, through the lower critical solution temperature boundary markedLCST, to a two-phase (L—L) region. (i.e. for a given temperature, thepressure starts at a pressure above the highest of thepressure-temperature curves representing the upper critical solutiontemperature (UCST), the LCST, and the vapor pressure, and the pressureafter the let-down for the given temperature is below thepressure-temperature curve representing the spinodal boundary and abovethe pressure-temperature curve representing the vapor pressure) Thepressure drop is sufficiently fast to avoid formation of a continuouspolymer and to form a discontinuous solvent/monomer phase. The pressuredrop across the region bounded by the LCST (binodal) boundary and thespinodal boundary must be especially rapid to induce phase separation byspinodal decomposition, which leads to rapid phase separation andsettling.

Level X is above another phase boundary marked Vapor pressure belowwhich the mixture enters a V-L-L region in which it is part vapor, andpart two phase liquid. The pressure at level X at the exit of theseparator is sufficiently high so that no vapor is formed.

Inside the separator (14) an upper lean phase is formed with less than0.1 wt % of polymer and a lower polymer rich phase with 30 to 40 wt % ofpolymer. The concentration is approximately double to triple that of thepolymerization mixture fed to the separator (14). After further removalof solvent and monomer in the low-pressure separator (34) and theextruder (40), polymer can be removed from the plant containing lessthan 1 wt %, preferably with 0.3 wt % or less, even more preferably <0.1wt % of volatiles, including water.

If the use of the plant is now compared with the row in Table 1 markedelastomer, it can be seen that although the polymerization temperatureis lower than for plastomer, and the polymer concentration emerging fromthe reactor is lower (its viscosity will be similar to that forplastomers), the same separation process and plant can be used to givean output which is somewhat lower (reflecting the reduced efficiency ofthe polymerization process at lower temperatures). With two reactors inseries, the disclosure of WO 99/45047 (Harrington et al.) may be used,which document is incorporated herein for purposes of US law. Generallyspeaking, in a series layout it is preferable that the first reactoroperates at temperatures between 0 to 110° C. and the second reactoroperates between 40 to 140° C. Preferably the first reactor operates attemperatures between 10 to 90° C. and the second reactor operatesbetween 50 to 120° C. Most preferably, the first reactor operates attemperatures between 20 to 70° C. and the second reactor operatesbetween 60 to 110° C. With appropriate control of process conditions andpoison levels temperature of this order of magnitude can also beobtained where one reactor only is used or two reactors are used underthe same process conditions.

The same can be said about the row in Table 1 marked “Predominantpropylene content copolymer” where the temperature is lowered to allowthe less reactive propylene monomer to form a sufficiently highmolecular weight. The general conditions described in WO 00/01745, whichare fully incorporated herein by reference for purposes of US patentpractice, can be used. In the runs, the polymerization temperaturevaried between 28 and 70° C.

While the process windows have been illustrated using prior artdisclosures which suggest metallocene selection and the suitableoperating window for a given polymer type, to the extent that priorpublished patent specifications are used to assist in such illustration,it should be kept in mind that these patent specifications did notprovide the separation and recycle and purification conditions in acontinuous plant with a recycle permitting full exploitation of theproduct capabilities of high activity metallocene catalyst systems atwhich the invention is best operated. The invention provides a plant andprocess which uses the given metallocene catalyst systems disclosed tomake the target polymers at high metallocene activity, under a widerange of polymerization conditions and with considerable energy andinvestment savings.

Advantages

It can be seen that the plant and process illustrated above in anon-limiting manner, permit polymerization and subsequent polymerseparation across a broad range of temperatures to yield polymers ofwidely varying average molecular weights and comonomer contents withcatalyst optimized for operation at low or high operating temperatures.A process plant according to the invention is capable of production ofplastomers, elastomers, and predominant propylene content copolymers bychanging only the substituents of the reaction mixture and the processconditions.

The plant has a low energy consumption because the extent of feedrefrigeration and re-pressurizing by pumping can be greatly reduced.Furthermore, no heat of vaporization is required to separate the polymerrich and polymer lean phases in the separator (14), and the heat in thelean phase is efficiently used to increase the temperature of thepolymerization mixture entering the separator (14). Little solvent andmonomer has to be purged to atmosphere. The evaporated materialsrecovered from the low pressure separator (34) can be fractionated toallow its direct purification without intervening condensation in afractionating tower and at the same time assisting the flow of the finalpolymer/solvent mixture before extrusion into the extruder to minimizepumping requirements. Variation in the pressure of the low-pressureseparator (34) may be used to control viscosity of the polymer/solventmixture into the devolatizer (40), thereby extending the range ofpolymers that can be processed to those with very high molecular weight.

Widely varying molecular weights and molecular weight distribution canbe obtained using the hydrogen stripping arrangement which can be simplyintegrated and requires no additional extraneous materials or theevaporation of large volumes of recycled lean phase liquid.

All documents cited herein are fully incorporated by reference for alljurisdictions in which such incorporation is permitted and to the extentthey are not inconsistent with this specification. All documents toshich priority is claimed are fully incorporated by reference for alljurisdictions in which such incorporation is permitted. Althoughdependent claims have single dependencies in accordance with U.S.practice, each of the features in any of the dependent claims can becombined with each of the features of one or more of the other dependentclaims dependent upon the same independent claim or claims.

1. A process for continuous solution polymerization of a feed ofolefinically unsaturated monomer in a hydrocarbon solvent underpressure, having a continuous stirred tank reactor arrangement to whicha single site catalyst is supplied, to form a polymer containingpolymerization reaction mixture, and downstream thereof separating meansfor continuous separation of the solvent and unreacted monomer from themixture, which separating means includes at least an initial liquidphase separator to separate the polymerization mixture into a lean phaseand a concentrated phase wherein A) a high capacity, low viscosity pumpraises the pressure of the feed to at least 75 bar and causes themixture to pass from the reactor arrangement through a heating stage upto a pressure reducing means upstream of the liquid phase separatorthrough the action of the pump and in the absence of further pumpingmeans between the reactor arrangement and the pressure reducing means;and B) a catalyst killer is added downstream of reactor arrangement andupstream of the liquid phase separator to suppress furtherpolymerization in the separator of the heated polymerization mixtureundergoing separation, the lean phase being passed through a cooler, andoptionally a drier, back to the inlet side of the pump; the concentratedphase being subjected to additional solvent removal downstream to obtaina solid polymer.
 2. The process of claim 1 in which a low pressureseparator receiving the concentrated phase from the liquid phaseseparator operates at a pressure of at least 2 bar gauge at a levelsufficient to convey the volatile phase removed from the concentratedphase to a fractionating tower for purification without further means ofcompression.
 3. The process of claim 1 in which the solvent is a lowboiling alkane based solvent and the polymer in the polymerizationmixture contains at least 50 mol % ethylene or propylene derived unitsout of the total monomers present.
 4. The process of claim 1 in whichthe polymerization mixture from the reactor arrangement is heated to thetemperature for separation in the separator successively by exchangersand the lean phase from the separator is used to supply heat to theupstream one of said heat exchangers.
 5. The process of claim 1 in whichthe lean phase is passed in liquid form to a means for removing hydrogenadded to or generated during polymerization, which means comprises ameans for contacting a stripping vapor with the lean phase in acountercurrent flow arrangement to concentrate the hydrogen in thevapour phase for removal from the lean phase recycle.
 6. A plant foroperating a continuous solution polymerization process of a feed ofolefinically unsaturated monomer in a hydrocarbon solvent underpressure, which plant contains a continuous stirred tank reactorarrangement to which a single site catalyst may be supplied to form apolymer containing polymerization reaction mixture, and downstream ofthe reactor arrangement separating means for continuous separation ofthe solvent and unreacted monomer from the mixture, which separatingmeans includes at least an initial liquid phase separator to separatethe polymerization mixture into a concentrated phase and a lean phase,wherein A) a high capacity, low viscosity pump is arranged for raisingthe pressure of the feed to at least 75 bar and a heating arrangement isprovided, to thereby cause the mixture to pass from the reactorarrangement through the heating arrangement up to a pressure reducingmeans upstream of the liquid phase separator (14), no additional pumpingmeans being provided between the reactor and the pressure reducingmeans; and B) means are provided for introducing a catalyst killerdownstream of reactor arrangement and upstream of the liquid phaseseparator to prevent further polymerization in the separator of theheated polymerization mixture undergoing separation, and means areprovided for cooling the lean phase, and means are provided forconveying a recycled stream back to the inlet side of the pump.
 7. Aprocess for continuous solution polymerization of a feed of olefinicallyunsaturated monomer in a hydrocarbon solvent under pressure, having acontinuous stirred tank reactor arrangement, to which a single sitecatalyst is supplied, to form a polymer containing polymerizationreaction mixture, and downstream thereof separating means for continuousseparation of the solvent and unreacted monomer from the mixture, whichseparating means includes at least an initial liquid phase separator toseparate the polymerization mixture into a lean phase and a concentratedphase, wherein A) a pump maintains a pressure of at least 75 bar in thepolymerization reactor and the temperature in polymerization reactorarrangement is maintained lower than or the same as that in theseparating means and a heating arrangement is provided upstream of theseparating means to optionally heat the reaction mixture to raise thetemperature in the separating means so that, upon a pressure drop via apressure reducing means upstream of the separator, the mixture passesthrough the lower critical solution phase boundary regardless of theinitial polymerization temperature; and B) a catalyst killer is addeddownstream of reactor arrangement and upstream of the liquid phaseseparator to suppress further polymerization in the separator of theheated polymerization mixture undergoing separation, the lean phasebeing passed through a cooler, and optionally a drier, back to the inletside of the pump; the concentrated phase being subjected to additionalsolvent removal downstream to obtain a solid polymer.
 8. The process ofclaim 7 in which the liquid phase separator and a low pressure separatorreceiving the concentrated phase from the liquid phase separator operateat a pressure of at least 2 bar gauge, at a level sufficient to conveythe volatile phase removed from the concentrated phase to afractionating tower for purification.
 9. The process of claim 7 in whichthe solvent is a low boiling alkane based solvent and the polymer in thepolymerization mixture contains at least 50 mol % ethylene or propylenederived units out of the total monomers present.
 10. The process ofclaim 7 in which the polymerization mixture from the reactor arrangementis heated to the temperature for separation in the separatorsuccessively by exchangers and the lean phase from the separator is usedto supply heat to the upstream one of said heat exchangers.
 11. Theprocess of claim 7 in which the lean is passed in liquid form to a meansfor removing hydrogen added to or generated during polymerization, whichmeans comprises a means for contacting a stripping vapor with the leanphase in a countercurrent flow arrangement to concentrate the hydrogenin the vapour phase for removal from the lean phase recycle.
 12. Aprocess plant suitable for continuous circulation of a solutionpolymerization reaction mixture, said plant comprising: a) a pressuresource, b) a polymerization reactor, downstream of said pressure source,c) a heat exchanger, downstream of said polymerization reactor, d) apressure let-down device, downstream of said heat exchanger, saidlet-down device capable of reducing the pressure of the reaction mixtureat a selected temperature pressure-temperature curve to a pressure belowthe spinodal boundary pressure temperature curve at a rate of at least20 bar/second, and e) a separator, downstream of said pressure let-downdevice, wherein said pressure source is sufficient to provide pressureto said reaction mixture during operation of said process plant toproduce a single-phase liquid reaction mixture in said reactor and atwo-phase liquid-liquid reaction mixture in said separator in theabsence of an additional pressure between said reactor and saidseparator.
 13. The process plant of claim 12 wherein said plant iscapable of production of plastomers, elastomers, or predominantpropylene content copolymers by changing only the substituents of thereaction mixture and the process conditions.
 14. A process forcontinuous solution polymerization of a feed of olefinically unsaturatedmonomer in hydrocarbon solvent under pressure, having a continuousstirred tank reactor arrangement, to which a single site catalyst assupplied, to form a polymer containing polymerization reaction mixture,and downstream thereof separating means for continuous separation of thesolvent and unreacted monomer from the mixture, which separating meansincludes at least an initial liquid phase separator to separate thepolymerization mixture into a lean phase for passing through a recycleback to the reactor arrangement and a concentrated phase, wherein thelean phase is passed in liquid form to a means for removing hydrogenadded or generated during polymerization, which means comprises a forcontacting a stripping vapor with the lean phase in a countercurrentflow arrangement to concentrate the hydrogen in the vapour phase forremoval from the lean phase recycle.
 15. The process of claim 14 whereinthe stripping vapor comprises ethylene for use in subsequentpolymerization.
 16. The process of claim 14 wherein a pair of reactorsare arranged in series and hydrogen is added to the downstream reactorto produce a lower molecular weight fraction.
 17. A plant for continuoussolution polymerization of a feed of olefinically unsaturated monomer ina hydrocarbon solvent under pressure, having a continuous stirred tankreactor arrangement, with inlets for feed and for a single sitedcatalyst components, to form a polymer containing polymerizationreaction mixture, and downstream thereof separating means for continuousseparation a the solvent and unreacted monomer from the mixture, whichseparating means includes at least an initial liquid phase separator toseparate the polymerization mixture into a lean phase for passingthrough a recycle back to the reactor arrangement and a concentratedphase, a conduit being provided for passing the lean phase in liquidform to a stripping arrangement for removing hydrogen added to orgenerated during polymerization, which stripping arrangement comprise ameans for contacting a stripping for with the lean phase in acountercurrent flow arrangement to concentrate the hydrogen in thevapour phase for removal from the lean phase recycle.